The invention relates to the shield of components made of thermoplastics in particular against such heating which might result in damages to the component, mechanical damages in particular.
A thermal shield for thermoplastic components has already been known, which consists of a thermally insulating mat which is not damaged even by the influence of the heat source, but prevents high temperatures from being dissipated towards the component to be protected. Such a thermally insulating mat is attached to the component by fasteners, for instance. If GMT carrier parts are used as components, they become too soft at temperatures exceeding 140xc2x0 C. It is very expensive and not too efficient to clip or fix aluminium sheet by riveting. If underbody coverings for motor vehicles are produced from the polycondensation product SMC, i.e. a polyester resin, and are protected against too great heating by the heat source like an exhaust silencer, for instance, different problems arise.
It is the object underlying the invention to provide a thermal shield or, respectively, a heat-proof component equipped therewith which is easy to manufacture, is as light-weight as possible, has not too great spatial dimensions and provides for a good thermal screening effect. Moreover, it is desired to use such materials which may be reused or disposed of in an environmentally friendly manner at low expenditure when the respective components are recycled, and to renounce the use of SMC materials.
The invention is claimed in claims 1 and 10 as well as in claim 13 in respect of the process for the manufacture thereof. Preferred embodiments may be taken from the subclaims and the following specification in conjunction with the drawing.
The principle for meeting this object in accordance with the invention consists in that an aluminium layer having a thermoplastic coating acts as a thermal shield in that the thermal shield serves as a connecting member to the structural unit which is to be protected and also consists of thermoplastic material on the outside. The thermoplastic coating connects with the thermoplastic material of the component to be protected via fusing, in particular, so that the thermal shield may very easily and quickly be attached to the outside of the component in situ, in particular. Such components are, for instance, underbody coverings for motor vehicles, which are to be protected against heat in the region of the exhaust silencer and the corresponding exhaust pipes, as well as engine compartment coverings. The invention also makes it possible that the thermal shield may be attached at the exact place. In contrast to expectations saying that a good heat-conducting material like aluminium may in any event not be used as a good thermal shield where thermoplastic layers instead of screws, clamps or the like are used as connecting elements since aluminium precisely leads the heat very well and quickly to the thermoplastic material of the xe2x80x9cconnecting layerxe2x80x9d, it was surprisingly observed that the opposite is true. Thus, there was no softening with a risk of the aluminium layer of components being detached in one embodiment, wherein polypropylene is used as a thermoplastic layer even if the aluminium side was heated to 160xc2x0 C. for one hour. It is assumed that the major part of the heat is dissipated by the aluminium, but is not dissipated to the thermoplastic material on the opposite side of the aluminium layer, but into the free, cooler space at a spacing from the heat source. In this respect, the aluminium layer no longer acts as a xe2x80x9cheat concentratorxe2x80x9d, but as a cooling member. It is therefore not only recommended to dispose the thermal shield in the immediate vicinity of the heat source, but to expand it slightly further into the low-temperature environment. It is also possible and useful, if need be, to structure the aluminium layer outside the actual heat region such that webs, which are more particularly free of lesser heat-conducting coatings, promote the cooling effect.
The aluminium layer should have a thickness between 20 xcexcm and 3 mm, more particularly between 0.08 and 0.2 mm. It is more particularly configured as a broad ribbon with a width of more than 10 cm. Both for the above-mentioned reasons in respect of cooling and for improving the mechanical stability, the aluminium layer may also be provided with web-shaped elevations and/or depressions and/or punctiform or, respectively, circular elevations.
The object is also met by an aluminium layer being structured to be net-shaped such that it is sufficiently self-supporting if no aluminium wires being too thin are used. Expanded aluminium metal in conjunction with the thermoplastic coating for instance meets the object underlying the invention.
The thermoplastic coating should consist of a polymerisation product like polypropylene, in particular, which behaves in a part-crystalline manner in the usual temperature ranges. This material is recommended above all when the component to be protected substantially consists of the same material too. Such a material may well be disposed of and also be reused, which is also true for aluminium. In this respect, superordinate economic and ecological requirements are also met. Polyester (PET), polyamide (PA) and thermoplastic polyurethane (TPU) are also suitable.
The thermoplastic coating should have a layer thickness between 10 pm and 5 mm, more particularly between 0.04 and 0.1 mm. The coating should have about half the thickness of the aluminium layer.
The principle according to the invention may not only be applied to the thermal shield as such, but to an aggregate wherein the thermal shield is combined to one structural unit together with the component to be protected. In this configuration of the invention, the thermal shield equally consists of an aluminium layer; this layer is connected with the carrier via a thermoplastic layer, the thermoplastic layer fusing with the thermoplastic material of the carrier.
The thermal shield is more particularly manufactured in that a thermoplastic coating is applied to the aluminium layer having a ribbon-shaped, a net-shaped or any other structure.
The aluminium layer is generally previously provided with the thermoplastic layer and then attached to the component.
A particularly favourable manufacturing process for a heat-proof component consists in that the aluminium layer is heated, via heat contact in particular, to a sufficiently high temperature which suffices for that a thermoplastic layer, which is pushed or, respectively, inserted or applied in a different manner between the aluminium layer and the component to be protected, connects, during pressing-on to the outside of the component by means of the aluminium layer, with said component and thereby sufficiently anchors the aluminium layer. In case an aluminium layer, which is smooth on the outside, does not meet these requirements, it is recommended to provide the layer with depressions and elevations by stamping, whereby the interface between the aluminium layer and the thermoplastic layer is enlarged and the adhesive forces are increased.
According to a further configuration of the invention, it is possible to provide web-like elevations on the component or, respectively, on a carrier part to be inserted between an additional intermediate component and the thermal shield, to which the thermal shield is fused, welded or glued if enough space is available. This achieves an additional sound-insulating or sound-absorbing effect and also improves the acoustically absorbing efficiency of the heat-proof component. This is above all useful for engine compartment coverings being configured as engine enclosures.